1. Field of the Invention
The present invention is directed to portable, network-independent electrical energy users, more particularly, however, to electrical handsets that are carried in the hand for use or during use.
2. Description of the Prior Art
Energy users or electrical handsets have an energy supply that is buffered by an energy store, which is usually rechargeable. Preferably rechargeable energy stores such as capacitors or accumulators, for example known nickel cadmium cells, are suitable in addition to non-rechargeable batteries such as alkali cells, zinc carbon batteries, or mercury button cells.
The maximum possible operating time of a network-independent energy user is dependent on the electrical power that the energy user uses in its operating conditions as well as on the capacity of the energy store that is built into the energy user. Since the usability and the competitiveness of the energy user also increase with an increasing operating time, there is a general desire to lengthen this by reducing the power consumed or by increasing the storage capacity of the energy store.
A further possibility for extending the network-independent operating time of a mobile energy user is to provide an additional photovoltaic energy supply. Given adequate light incidence, the photovoltaically generated energy can relieve, replace, and/or recharge the energy store.
Heretofore, high-performance solar cells having an efficiency above 15 percent have only been manufactured of crystalline semiconductor materials such as silicon (c-Si) or gallium arsenide. These materials, however, have the disadvantage that only planar or at most slightly curved solar cells can be manufactured therefrom, because such known solar cells are not capable, or are only insufficiently capable, of being bent due to the fragility of the crystalline semiconductors and the lack of flexibility deriving therefrom.
The employment of high-performance solar cells in mobile energy users has thus hitherto been dependent on making an adequately flat and free surface available at the user that can be equipped with planar, crystalline solar cells. In smaller mobile electrical users, and in particular in electrical handsets, however, the surface on which solar cells can usually be applied is limited. Without enormous added outlay, moreover, it is not possible to provide recesses in the solar cell in order to create space for raised or sunken parts or to create access to functional parts such as keys or switches. The occupation of the flat and free surface of the electrical energy user that is available is therefore usually only possible with solar cells that are fashioned approximately rectangular or round.
A further problem is that, due to the fragile nature of the crystalline solar cells, an increased thickness of the material for the support and/or covering of the solar cell is required, which causes additional weight for the portable energy user.